This invention relates to current shunts for measuring current in a circuit.
A current shunt is essentially a low value resistance element connected in a circuit as a means of sensing a measuring current. For measuring high currents, the resistance element may simply be a strip of metallic conductor with voltage sensing points at each end and a defined resistance between the two voltage sensing points. The current flowing through the shunt is calculated by measuring the voltage drop across the shunt, that is, between the two voltage sensing points, and dividing the voltage by the resistance of the shunt. A copper shunt suffers from a large change in resistance due to temperature. A significant current measurement error occurs if a fixed value for resistance is used in the calculation of the current through such a shunt. Typically, this error is large, as much as 35 percent over 0 degrees celsius to 100 degrees celsius. In the prior art, this effect is overcome by using a more expensive material such as manganin instead of copper, the manganin having a much smaller change in resistance with temperature.
The use of a separate, more expensive material, obviously adds expense to the measurement device, but also adds mechanical connections between existing circuit components and the more expensive material. The addition of mechanical connections, increases resistance and increases susceptibility to problems due to corrosion, oxidation, mechanical fatigue and the like.
It would be desirable, therefore, to sense current through an existing circuit component without the need for additional mechanical connections, and without the need for a more expensive material with a small resistance-temperature coefficient. The present invention addresses this need.